1. Field of the Invention
The present invention relates to a laminated ceramic electronic component and a manufacturing method therefor, and more particularly, relates to a laminated ceramic electronic component which has an external terminal electrode formed directly by plating so as to be electrically connected to an internal electrode, and a method for manufacturing the laminated ceramic electronic component.
2. Description of the Related Art
As shown in FIG. 3, a laminated ceramic electronic component 101 as typified by a laminated ceramic capacitor includes a component main body 105 including a stack structure including a plurality of stacked ceramic layers 102 made of, for example, a dielectric ceramic, and including a plurality of layered internal electrodes 103 and 104 disposed along the interfaces between the ceramic layers 102. The ends of the plurality of internal electrodes 103 and the ends of the plurality of internal electrodes 104 are respectively exposed at end surfaces 106 and 107 of the component main body 105, and external terminal electrodes 108 and 109 are arranged respectively so that the respective ends of the internal electrodes 103 and the respective ends of the internal electrodes 104 are electrically connected to each other.
For the formation of the external terminal electrodes 108 and 109, typically, a metal paste including a metal constituent and a glass constituent is applied onto the end surfaces 106 and 107 of the component main body 105, and then fired to form paste electrode layers 110. Next, first plating layers 111 including, for example, nickel as their main constituent are formed on the paste electrode layers 110, and second plating layers 112 including, for example, tin or gold as their main constituent are formed on the first plating layers 111. More specifically, each of the external terminal electrodes 108 and 109 includes a three-layer structure of the paste electrode layer 110, the first plating layer 111, and the second plating layer 112.
The external terminal electrodes 108 and 109 are required to provide favorable solderability when the laminated ceramic electronic component 101 is mounted on a substrate using solder. At the same time, the external terminal electrode 108 is required to electrically connect the plurality of internal electrodes 103 to each other, which are electrically insulated from each other, and the external terminal electrode 109 is required to electrically connect the plurality of internal electrodes 104 to each other, which are electrically insulated from each other. The second plating layer 112 ensures solderability, and the paste electrode layer 110 electrically connects the internal electrodes 103 and 104 to each other. The first plating layer 111 prevents solder leach in the solder joint.
However, the paste electrode layers 110 each have an increased thickness of several tens of micrometers to several hundreds of micrometers. Therefore, in order to provide the dimensions of the laminated ceramic electronic component 101 within certain specifications, there is need to reduce the effective volume for providing the capacitance, because the volume of the paste electrode layers 110 must be provided. On the other hand, the plating layers 111 and 112 each have a thickness on the order of several micrometers. Thus, if the external terminal electrodes 108 and 109 can be made only of the first plating layer 111 and the second plating layer 112, the effective volume for providing the capacitance can be increased.
For example, International Publication No. 2008/059666 discloses plating layers defining external terminal electrodes, which are formed directly on end surfaces of a component main body. Furthermore, International Publication No. 2008/059666 also discloses the formation of interdiffusion regions in boundary sections between internal electrodes and the plating layers by performing a heat treatment after the formation of the plating layers.
Therefore, the application of this conventional art produces a volume expansion of the metal in the interdiffusion regions, which effectively fills gaps which may be present at the interfaces between the ceramic layers and each of the internal electrodes and external terminal electrodes, and advantageously prevents a plating solution in plating processing which may be performed subsequently and other moisture from penetrating into the component main body.
In addition, the application of this conventional art is expected to improve the bonding strength at the interfaces between the ceramic material of the ceramic layers stacked with the internal electrode therebetween and the plating layers in the component main body. Furthermore, when requiring an improvement of the bonding strength, it is believed that a heat treatment is preferably performed at a temperature of not less than 1000° C. which is the eutectic temperature of the metal defining the plating layers. For example, when forming a copper plating layer, it is believed that a heat treatment is preferably performed at a temperature of not less than 1000° C. which is close to the eutectic temperature of copper.
However, the heat treatment performed at a temperature of 1000° C. or more may encounter a problem of the copper being partially melted. As a result, when the laminated ceramic electronic component is mounted on a circuit board using solder, the bonding strength to the circuit board may be decreased.
In addition, when forming a plating layer, such as nickel on the copper plating layer, the adhesion force to the copper plating layer may be decreased.